There are devices already available which are used to transfer power through magnetic induction. These devices normally consist of a primary unit having a primary coil. The primary coil generates a magnetic field. A secondary unit separable from the primary unit comprises a secondary coil. When the secondary coil is placed in proximity to the varying magnetic flux created by the primary coil, the varying magnetic flux induces an alternating current in the secondary coil thus transferring power inductively from the primary unit to the secondary unit. Generally, the secondary unit supplies the transferred power to an external load, for example, to a rechargeable battery. The secondary unit may be carried in host object which includes the load.
A problem in such devices is that it is generally not possible to mechanically prevent foreign objects made of metal from being placed into proximity with the primary coil and getting coupled to the primary coil. The varying magnetic field in the primary coil may induce current in the foreign objects made of metal. Such currents may cause power losses that may also cause heating of the object.
There are already different methods available to detect a foreign object placed in the proximity of the above devices. For example, WO2009081115 discloses such a device and method to detect a foreign object in the inductively coupled devices.